Brachytherapy is a general term covering medical treatment which involves the placement of a radioactive source near a diseased tissue and may involve the temporary or permanent implantation or insertion of a radioactive source into the body of a patient. The radioactive source is thereby located in proximity to the area of the body which is being treated. This has the advantage that a high dose of radiation may be delivered to the treatment site with relatively low dosages of radiation to surrounding or intervening healthy tissue.
Brachytherapy has been proposed for use in the treatment of a variety of conditions, including arthritis and cancer, for example breast, brain, liver and ovarian cancer and especially prostate cancer in men (see for example J. C. Blasko et al., The Urological Clinics of North America, 23, 633-650 (1996), and H. Ragde et al., Cancer, 80, 442-453 (1997)). Prostate cancer is the most common form of malignancy in men in the USA, with more than 44,000 deaths in 1995 alone. Treatment may involve the temporary implantation of a radioactive source for a calculated period, followed by its removal. Alternatively, the radioactive source may be permanently implanted in the patient and left to decay to an inert state over a predictable time. The use of temporary or permanent implantation depends on the isotope selected and the duration and intensity of treatment required.
Permanent implants for prostate treatment comprise radioisotopes with relatively short half lives and lower energies relative to temporary sources.
Examples of permanently implantable sources include iodine-125 or palladium-103 as the radioisotope. The radioisotope is generally encapsulated in a casing such as titanium to form a “seed” which is then implanted. Temporary implants for the treatment of prostate cancer may involve iridium-192 as the radioisotope.
Conventional radioactive sources for use in brachytherapy include so-called seeds, which are sealed containers, for example of titanium, containing the radioisotope within a sealed chamber but permitting radiation to exit through the container/chamber walls (U.S. Pat. No. 4,323,055 and U.S. Pat. No. 3,351,049). Such seeds are only suitable for use with radioisotopes which emit radiation which can penetrate the chamber/container walls. Therefore, such seeds are generally used with radioisotopes which emit γ-radiation or low-energy X-rays, rather than with β-emitting radioisotopes.
Radioactive seeds are generally loaded into needles, with the needles then being inserted into the treatment site, such as prostate, using ultrasound imaging to guide the insertion process. The radioactive seeds are either positioned independently within the needles and hence are located independently within the treatment site after they have been moved out of the needle, or they are connected in a string arrangement by being loaded within a hollow, absorbable suture member.
U.S. Pat. No. 5,460,592 discloses a method and apparatus for transporting a radioactive device. The device comprises a flexible, elongated woven or braided bio-absorbable carrier material having spaced radioactive seeds disposed therein. On heating, the carrier material holding the seeds becomes semi-rigid. A length of the semi-rigid carrier material with radioactive seeds disposed therein may then be loaded into a conventional, hollow metal dispensing needle or applicator cartridge which is used to implant the radioactive seeds into or contiguous to the treatment site, for example a tumour.
A commercial product consisting of iodine-125 seeds regularly spaced at between 0.6 and 1.2 cm centre to centre inside a braided, semi-rigid bioabsorbable suture material is available from Medi-Physics Inc. under the trade name I-125 RAPID Strand™. This product may be used to treat conditions such as head and neck cancers, including those of the mouth, lips and tongue, brain tumours, lung tumours, cervical tumours, vaginal tumours and prostate cancer.
One advantage of this type of suture/radioactive seed combination is that the radioactive seeds are implanted or inserted into a patient with a pre-determined spacing, depending on their spacing in the suture material. The bioabsorbable material is then slowly absorbed into the patient's body to leave the spaced seeds in position. This predetermined spacing and the semi-rigid nature of the suture aids a physician in calculating both the total radiation dose and the dose profile which will be delivered by the seeds inside a patient's body, and also aids in accurate placement of the seeds. In addition, more than one seed is implanted at once, so lessening the time taken for implantation over that required for the placement of individual loose seeds. The risk of seed migration away from the site of implantation is also reduced (Tapen et al., Int. J. Radiation Oncology Biol. Phys., vol. 42(5), pages 1063-1067, 1998).
Another advantage of the hollow suture combination over independent seeds approach is that the independent seeds, even once in the treatment site, for example prostate, could migrate out of the prostate to various other locations in the body, including lungs. Migrated seeds can reduce implant quality and also potentially harm the patient.
However, this hollow suture combination has limitations on long axis strength due to the void areas, introduced into the arrangement during manufacturing, used for the spacing between the radioactive seeds. This void area long axis strength is limited to the strength of the suture material. Although the void area strength is increased during the heat stiffening manufacturing process, the resulting strength is still not ideal. Due to this limitation, the suture combination can sometimes jam within the insertion needle, resulting in a collapsing of the suture combination in the void area between the radioactive seeds. This condition requires removal of the needle from the prostate and the subsequent reloading of the needle with independent radioactive seeds. This alteration of technique is time-consuming and expensive in nature.
One approach to remedy the situation is disclosed in U.S. Pat. No. 6,264,600. It discloses a method and apparatus including a hollow suture with alternating plurality of radioactive seeds and intermediate spacers. While this suture/seed combination offers stronger long axis strength, there are several areas that can be improved upon.
First, there is still need for even more long axis strength to reduce the possibilities of suture jamming within the insertion needle.
Further, both hollow suture/seed combination and current hollow suture/seed/spacer combination is singular in color, with only dimensional differences in seeds and void areas of the assembly. This limitation can cause uncertainty in preparing the combination in implant. The current fixture only allows cutting in the void areas of the suture combination, away from the critical radioactive seed component. However, this becomes impossible once the suture combination is removed from the fixture.
Finally, current suture/seed/spacer combination has similar diameters for both seed and spacer. This lack of dimensional difference makes cutting more difficult.
There is therefore a need for an improved radioactive source which does not suffer from all the disadvantages of the known sources, and which can preferably be produced using an automated manufacturing process.